According to Reuters the toning category's dizzying growth -- from $17 million in 2008 to $245 million in 2009, according to research firm NPD Group -- is in sharp contrast to the 1.4 percent decline in overall athletic footwear sales in 2009.

And although toning shoes make up just a small part of the overall $18.6 billion U.S. athletic shoe market, they drove sales gains over the holidays. This month it was estimated $1 billion in toning shoe sales in 2010.

Interestingly with Reebok, Sketchers & Adidas all onboard, Nike - the global leader in athletic footwear – is nowhere to be found?

"They should have been on this sooner and they're playing catch-up now," said analyst Matt Powell of research firm SportsOneSource. "Clearly, Nike is losing significant market share."

Powell estimates that Nike took a 20 percent market share loss in women's footwear in the fourth quarter due to what he called a "lack of focus on the female customer."

I’ve tried the Sketchers Shape-Ups & while the promotional material claims the wearer will lose weight & tone while doing normal activity, I remain skeptical. You can definitely feel the difference in posture but I think the main difference was that I was far more conscious of how I use my body when wearing them. (As well as being self conscious, these shoes are NOT pretty)!

They’re sure hard to miss in the US, every sports store we entered or walked past seemed to be dedicating significant shelf & window time to these specimens.

It seems these shoes are marketed to primarily women, who aren’t actually interested in breaking any kind of sweat whilst exercising, with the likes of Reebok touting "EasyTone" shoes, meanwhile, help you "get better legs and a better butt with every single step."

However unattractive, this is definitely a growing market with both men & children ripe for the picking.